Helical tooth broach

ABSTRACT

A helical gear tooth broach is provided which does not require to clamp strongly the work to be broached by a special clamping device, and which does not perform an intermittent cutting action against the work. A gear tooth broach is provided having an elongate body having a series of axially aligned and spaced teeth disposed thereon. The direction of tooth spaces or traces of the teeth in a longitudinally extending helical alignment and the direction of the gullets of the teeth in a general side by side circumferentially extending helical arrangement are both oriented to the same hand of helix angle.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a gear tooth broach for forming internal helical gears or splines.

[0003] 2. Description of the Related Art

[0004] Internal helical gears or splines widely used in transmissions for motor cars are machined by using helical gear tooth broaches each having a series of axially aligned and spaced teeth disposed thereon, tooth spaces or traces of the teeth in a longitudinally extending helical alignment along the axis of the body at a helical angle the same as that of the internal helical gear or spline to be machined and gullets of the teeth in a general side by side circumferentially extending helical arrangement.

[0005] Generally, the helical gear tooth broach has an elongate body having a roughing broach section disposed thereon having a series of teeth having substantially the same width and increasing height to perform deep cut of the tooth spaces and a finishing broach section formed on a shell integrated with the elongate body and having a series of teeth having substantially full height and increasing width to perform finish cut of the sides of each tooth of a work piece.

[0006] A helical gear tooth broach, such as shown in Japanese Industrial Standard (JIS) B 0175 No. 1622, is of so called a right-angled-to-the-axis gullet broach, wherein each tooth space or trace of the teeth is formed so that it longitudinally extends at a helical angle the same as that of an internal helical gear or a work to be machined, and each gullet of the teeth in a general side by side circumferentially extending helical arrangement is made to form an annular groove. Such a right-angled-to-the-axis gullet broach performs an intermittent cutting action against horizontal plane of the work to be machined, and generates vibrations and deteriorates machining accuracy.

[0007] Further, as shown in FIG. 4 of U.S. Pat. No. 2,986,801, a helical gear tooth broach is known which has a series of axially helically aligned and spaced thread-like teeth along the axis of the broach body and gullets of the teeth each of which extends at a helical angle perpendicular to the helix angle of a tooth space or trace. More precisely, in the FIG. 4 of U.S. Pat. No. 2,986,801, the direction of the arrow 7 of a tooth space or trace crosses at a right angle to the direction of the arrow 6 of a gullet. This type of broach is called right-angled-to-the-tooth-trace gullet broach.

[0008] Furthermore, Japanese Unexamined Patent Publication (TOKKAI) Hei 2(1990)-15915 and TOKKAI Hei 1(1989)-271119 both disclose helical gear tooth broaches having gullets each of which extends at a helical angle not perpendicular to the helix angle of a tooth space or trace. Also, in Japanese Examined Utility Model Publication Hei 8(1996)-8019 and TOKKAI Hei 10(1998)-309622, helical tooth broaches are disclosed in which the number of each of its helical-splined gullet(s) is changed.

[0009] However, in the above described conventional helical gear tooth broaches, such as shown in FIG. 4 of this application, the direction of the tooth spaces or traces 14 in the longitudinally extending helical alignment and the direction of the gullets 13 in the general side by side circumferentially extending helical arrangement are revesely oriented to each other, that is, that of the tooth spaces or traces 14 orients to a right hand of helix angle (right-upward oriented) and on the contrary, that of the gullets 13 directs to a left hand of helix angle (left-upward oriented).

[0010] Setting the helix angle β of a tooth space or trace 14 of the teeth 12 to be equal to that of the work to be broached, and assuming that the helix angle of a gullet 13 is (90°-α′), by selecting the helix angles β, α′ and the number of helically splined gullet(s) the cutting dimension of the broach are determined. In the above described right-angled-to-the-axis gullet broach, the angle α′ is set to be equal to 0 (α′=0), and in the above described right-angled-to-the-tooth-trace gullet broach, α′=β. Further, the helix angle β of the tooth space or trace 14 is called as “a helix angle to the axis of the broach”, and the helix angle (90°-α′) of the gullet 13 is called as “a helix angle to the circumferential direction of the gullet 13”.

[0011] When an internal helical gear or a work is broached using a helical gear tooth broach, a twisting movement is applied to the work along the direction of the helix angle β of the tooth spaces or traces 14 of the broach, resulting that the work to be broached is rotated in a direction in which the twisting movement is applied to the broach.

[0012] In such a situation, in the above described conventional helical gear tooth broach having the conventional helical gullet, such as shown in FIG. 4, a component of the force generated by the cutting resistance force of the teeth of the broach in an axial direction presses the work to be broached in a direction circumferentially and to additionally rotate thereof to a greater or lesser extent. To cope with this component of the force, the work to be broached should be strongly clamped to limit the rotating movement thereto.

[0013] On the other hand, in the above described right-angled-to-the-axis gullet broach, since the angle α′=0, no component of the force generated by the cutting resistance force of the teeth and no circumferentially additional rotational force is applied to the work to be broached. However, such broach performs an intermittent cutting action against the work and deteriorates machining accuracy compared with the above described right-angled-to-the-tooth-trace gullet broach.

[0014] Therefore, in the above described conventional helical gear tooth broaches, in order to limit the rotating movement of the work to be broached, a strong clamp on the work is required. On the contrary, in the above described right-angled-to-the-axis gullet broach, although no component of the force is applied, performs an intermittent cutting action against the work, and no sufficient machining accuracy is obtained.

SUMMARY OF THE INVENTION

[0015] It is an object of this invention to provide a helical gear tooth broach which does not require to clamp the work to be broached strongly by a special clamping device, and which does not perform an intermittent cutting action against the work.

[0016] These and other objects of the present invention will be solved by a gear tooth broach for broaching internal helical gears or splines comprising an elongate body having a series of axially aligned and spaced teeth disposed thereon, tooth spaces or traces of the teeth in a longitudinally extending helical alignment along an axis of the body and gullets of the teeth in a general side by side circumferentially extending helical arrangement. The gear tooth broach is characterized in that a first direction of the tooth spaces or traces of the teeth in the longitudinally extending helical alignment and a second direction of the gullets of the teeth in the general side by side circumferentially extending helical arrangement are both oriented to the same hand of helix angle (right-upward or left-upward oriented).

[0017] Since, in the above described conventional helical gear tooth broaches, such as shown in FIG. 4 of this application, the direction of the tooth spaces or traces in the longitudinally extending helical alignment and the direction of the gullets in the general side by side circumferentially extending helical arrangement are revesely oriented to each other, the rotational force applied to the work generated by the component of the force generated by the cutting resistance force of the teeth of the broach in a direction circumferentially and the rotational force by the pulling force applied to the broach along the tooth spaces, act in the same rotational direction and increase the rotational force applied to the work.

[0018] On the contrary, according to this invention, since the direction of the tooth spaces or traces in the longitudinally extending helical alignment and the direction of the gullets in the general side by side circumferentially extending helical arrangement are both oriented to the same hand of helix angle (right-upward or left-upward oriented), the rotational force applied to the work by the twisting movement along the direction of the tooth spaces or traces, and the rotational force applied to the work generated by the component of the force of the cutting resistance force of the teeth by the pulling force applied to the broach, act in the reverse rotational direction to each other, thereby decreases the rotational force applied to the work. That is, a component of the force generated by the cutting resistance force effects to prevent the rotational movement of the work by the twisting movement along the direction of the tooth spaces or traces, and stable cut of the broach is achieved. Thus, the helical gear tooth broach according to the present invention does not require to clamp strongly the work to be broached by the special clamping device, Further, because of that the gullets are helically arranged in contrast to the above right-angled-to-the-axis gullet broach, no intermittent cutting action against the work is performed.

[0019] Preferably, assuming that a helix angle of the direction of a tooth space is β and the helix angle of a gullet is (90°-α), the angle α is determined to range 0°<α≦β+5°.

[0020] The reason that the angle α of the helix angle (90°-α) of the gullet is determined to range equal to or less than (β+5°), lies in that if the angle α is above (β+5°), dulls sharpness of the teeth, and detrorates surface roughness resulting short life thereof. More preferably, the angle α is made equal to the angle β , so that α=β.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a general elevational front view of a gear tooth broach according to a preferred embodiment of the present invention in which a direction of a tooth space or trace and a direction of a gullet are both oriented to the same right hand of helix angle (right-upward oriented).

[0022]FIG. 2 is a development view into a plane surface of a portion of the broach shown in FIG. 1 showing a series of axially aligned and spaced teeth disposed on the broach having both tooth spaces and gullets.

[0023]FIG. 3 is an enlarged view of one of the teeth of the gear tooth broach shown in FIG. 2 together with diagrammatic representation of the cutting force N, components both of the cutting force N in an axial direction F and that of in a circumferential direction RT all applied to the a work to be broached by a tooth edge of a tooth.

[0024]FIG. 4 is a development view into a plane surface similar to FIG. 2 of a portion of a conventional broach showing a series of axially aligned and spaced teeth disposed on the broach having both tooth spaces or traces in a longitudinally extending helical alignment at a right hand of helix angle (right-upward oriented) and gullets in a general side by side circumferentially extending helical arrangement at a left hand of helix angle (left-upward oriented).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] While the present invention is applicable to the cutting of internal gears or splines by means of a broach or to the broaching of external gears or splines by a pot broach, and while it is applicable to a solid broach having both a roughing section and a finishing section or a broach having a finishing section on a shell provided at the trailing end of a roughing section of an elongate body, it may be assumed in the following description that a preferred embodiment of the present invention will be given with reference to the cutting of internal gears by means of a solid broach having both a roughing section and a finishing section shown in FIGS. 1-3.

[0026]FIG. 1 is a general elevational front view of a gear tooth broach 10 according to the preferred embodiment of the present invention in which a direction of a tooth space or trace and a direction of a gullet are both oriented to the same right hand of helix angle (right-upward oriented). In FIG. 1, the gear tooth broach 10 for broaching of internal helical tooth traces of works of internal helical gears not shown comprises an elongate body 1 having a series of axially aligned and spaced teeth 2 disposed thereon along an axis 5 of the body 1, tooth spaces 4 in longitudinally extending at a helical angle β the same as that of the internal helical gears to be machined not shown, and gullets 3 in general side by side circumferentially extending at a helix angle α to a plane perpendicular to the axis 5.

[0027] The direction of the longitudinally helically extending tooth spaces 4 is made to orient at the same right-hand helix angle (right-upward oriented) with that of in side by side circumferentially helically extending gullets 3. The broach 10 is pulled downwardly as seen in FIG. 1, by a pulling device not shown and is formed on the solid elongate body 1 in series from the lower portion, a roughing broach section having a series of teeth 2 of substantially the same width and of increasing height to perform deep cutting of the tooth spaces of a work not shown, a semi-finishing broach section and a finishing broach section both having a series of teeth 2 of substantially full height and of increasing width to perform sides cutting of the tooth spaces of the work not shown. The broach 10 has a pull end 7 at its lowermost end and a follower end 6 at its uppermost end as seen in FIG. 1. The broach 10 may have all these broach section on the solid elongate body 1 or may have one of them thereon. Further, the finishing section may be formed on the solid elongate body 1 or on a detachable shell not shown provided at the trailing end of the roughing section formed on the solid elongate body 1.

[0028] Reference is made to FIG. 2 showing a development elevational view into a plane surface of a portion of the broach shown in FIG. 1, showing a series of axially aligned and spaced teeth 2 disposed on the elongate body 1 of the broach 10 having both tooth spaces or traces 4 and gullets, wherein the tooth spaces or traces 4 longitudinally extending at a helical angle β to the axis 5 of the broach 10, and the gullets 3 in general side by side circumferentially extending at a helix angle α to the perpendicular plane to the axis 5, and the helix angle to the axis 5 is (90-α), and the direction of the helix angle (90-α) is made to orient to the same right-hand of helix angle (right-upward oriented) with the helix angle β.

[0029] The cutting or broaching of an internal gear or work not shown by means of the broach 10 is performed by pulling the broach 10 downwardly as seen in FIG. 2 by a pulling device not shown and the broach 10 is simultaneously rotated so that the direction of tooth spaces or traces 4 of the broach 10 coincides with the longitudinal helical angle of the tooth spaces or traces of the internal gear or work to be broached not shown.

[0030] As seen in FIG. 3, the internal gear or work not shown is applied by the broach 10 according to the present invention, a twisting rotational force T and a cutting force F or a pulling force downwardly as seen in FIG. 2. However, since the direction of a leading tooth cutting edge 7 of the tooth 2 along the gullet 3 orients to the same right-hand of helix angle (right-upward oriented), the work is applied a component N of the cutting force F in a direction normal to the leading tooth cutting edge 7, a component F of the cutting force N in an axial direction and a rotational force RT of the cutting force N in a rightward direction or a cercumferential direction as seem in FIG. 3.

[0031] This results that against the twisting rotational force T applied to the work by the broach 10, a counter rotational force RT is applied to the same, thus, the twisting rotational force applied to the work by the broach 10 is decreased by the counter rotational force RT to be equaling to (T-RT), and reduces a clamping force to be applied to the work.

[0032] In contrast, in the above described conventional helical gear tooth broach shown in FIG. 4, the direction of the longitudinally extending helical tooth spaces or traces 14 and the direction of the side by side circumferentially extending helical gullets 13 are revesely oriented to each other. This will be explained if explained seeing the FIG. 3, that its leading cutting edge along a gullet will be oriented to left-upwardly, therefore, the direction of the twisting rotational force will be applied to the work left-upwardly. Assuming this left-upwardly oriented twisting rotational force LT, the twisting rotational force applied to the work by the broach 10 will reach to (T+LT). Thus, the decrease of the twisting rotational force applied to the work is computed in the following formula; (T+LT)−(T−RT)=(LT+RT). The amount of decrease (LT+RT) is of very large. Occasionally, the number of helically splined gullet(s) of a broach is usually selected to range three(3) to five(5), and in this embodiment, the number of helically splined gullets is shown as having three (3).

[0033] In short, in the gear tooth broach according to the present invention, the direction of the tooth spaces or traces in the longitudinally extending helical alignment and the direction of the gullets in the general side by side circumferentially extending helical arrangement are both oriented to the same hand of helix angle (right-upward or left-upward oriented), the twisting rotational force applied to the work generated by the cutting resistance force of the teeth of the broach actively functions to prevent the twisting rotational force applied to the work, thereby the clamping force to be applied to the work is made lesser, and does not require to clamp strongly the same by the special clamping device.

[0034] Generally, a work support jig of a broaching machine on which a work is placed is equipped thereon a special clamping device so called “spikes”, a device having a lot of needle-like spikes, like a pinholder, and broaching is performed by placing the work on the “spikes” set on the work support jig. However, in the above embodiment, since the twisting rotational force by the component applied to the work by the broach may be lessened to a degree that the frictional force between the work and the work support jig suffices the necessary clamping force, so that the work can be broached without using such a special clamping device so called “spikes”.

[0035] Further, since the direction of the tooth spaces in the longitudinally extending helical alignment and the direction of the gullets in the general side by side circumferentially continuously extending helical spline at an angle (90°-α) are both oriented to the same hand of helix angle (right-upward or left-upward oriented), very stable cut may be performed with high machining accuracy. Preferably, assuming that the helix angle of the direction of a tooth space is β and the helix angle of a gullet is (90°-α), the angle α is determined to range 0°<α≦β+5°, thereby the lowering or dulling of the sharpness of the broach teeth is prevented.

[0036] Further, in the broaching of the broach according to the present invention, each tooth continuously performs the same cutting action with the same cutting condition with those of the others, no intermittent cutting action is performed against the work in contrast to the right-angled-to-the-axis gullet broach, resulting that heat generation is decreased, accuracies both in tooth profiles and tooth spaces are much increased, further, since no intermittent cutting action is performed, service life is made longer than that of the right-angled-to-the-axis gullet broach. 

What is claimed is:
 1. A gear tooth broach for broaching internal helical gears or splines comprising an elongate body having a series of axially aligned and spaced teeth disposed thereon, tooth spaces or traces of the teeth in a longitudinally extending helical alignment along an axis of the body and gullets of the teeth in a general side by side circumferentially extending helical arrangement, characterized in that a first direction of the tooth spaces or traces of the teeth in the longitudinally extending helical alignment and a second direction of the gullets of the teeth in the general side by side circumferentially extending helical arrangement are both oriented to the same hand of helix angle (right-upward or left-upward oriented).
 2. A broach as defined in claim 1, in which assuming that a first helix angle of said first direction of a tooth space or trace is β and a second helix angle of a gullet is (90°-α), an angle α is determined to range 0°<α≦β+5°. 